In a semiconductor device, it is known to bond a cap substrate to a base substrate for protecting various element formed in a surface layer of the base substrate.
In such a semiconductor device, an electrical connection for electrically connecting the base substrate and an external part is necessary. For example, it is known to make a bonding wire directly on the surface of the base substrate through a through hole formed in the cap substrate. In such a method, however, a large through hole is required in the cap substrate to conduct wire bonding. That is, an area necessary for making the electrical connection is likely to increase.
In order to ease the electrical connection between the element and the external part by the wire bonding, soldering or the like in a small area, a leading electrode that extends from the base substrate to the surface of the cap substrate and allows the electrical connection at the end can be employed.
It has been known to use a portion of the cap substrate as the leading electrode. For example, the cap substrate made of silicon is divided into partial regions by an insulating and separating trench, and a specific region of the partial regions, which connects to an insulated and separated base semiconductor region of the base substrate, is used as a leading conductive region. The upper end of the specific region is electrically connected to the external part by the wire bonding, soldering or the like.
A semiconductor device having such an electrical connection structure is, for example, described in Japanese Patent Application Publications No. JP2008-229833A (Publication 1, corresponding to US2008/0290490A1) and No. JP2008-256495 (Publication 2).
FIG. 30 shows an example of the semiconductor device described in Publication 1. A semiconductor device 91 shown in FIG. 30 has a semiconductor base substrate B2 and a conductive cap substrate C2 bonded to the base substrate B2.
The base substrate B2 is a SOI (Silicon On Insulator) substrate in which an embedded oxide film 20 is interposed between a SOI layer 21 and a support substrate 22. Insulated and separated multiple base semiconductor regions Bs are formed in a surface layer of the base substrate B2. The base semiconductor regions Bs are provided by the SOI layer 21, and are insulated and separated from adjacencies by a trench 23 that reaches the embedded oxide film 20. Projections T1 are formed above the base semiconductor regions Bs. The projections T1 are provided by a conductive film 50, which is made of poly crystal silicone, metal or the like.
The semiconductor device 91 includes a mechanical quantity sensor element for measuring a mechanical quantity, such as acceleration and angular velocity, using an inertia force. The mechanical quantity sensor element is constructed of the multiple base semiconductor regions Bs. Specifically, the base semiconductor regions Bs include at least two base semiconductor regions Bs1 and two base semiconductor regions Bs2.
The base semiconductor regions Bs1 constitute a movable semiconductor region. The base semiconductor regions Bs1 are formed by performing sacrifice layer etching on a part of the embedded oxide film 20. The base semiconductor regions Bs1 as the movable semiconductor region include a movable electrode Em, which is formed to be displaceable.
The base semiconductor regions Bs2 constitute a fixed semiconductor region including a fixed electrode Es opposed to the movable electrode Em. The two base semiconductor region Bs1 and the two base semiconductor region Bs2 each form a continuous and integrated region on a plane.
In the semiconductor device 91, a capacitance is created between opposed surfaces of the movable electrode Em and the fixed electrode Es. As the movable electrode Em is displaced in a direction perpendicular to the opposed surfaces in accordance with the applied mechanical quantity, the capacitance changes in accordance with a change in the distance between the movable electrode Em and the fixed electrode Es Thus, the applied mechanical quantity is detected by measuring the change in capacitance.
The cap substrate C2 is provided by a single crystal silicon substrate 30 on which multiple cap conductive regions Ce as partial regions are formed. The cap conductive regions Ce are divided by an insulating and separating trench 31 that passes through the single crystal silicon substrate 30. The cap substrate C2 has a surface protection layer 33 made of silicon oxide (SiO2) or the like, and electrode pads 34 made of aluminum (Al) or the like.
The cap substrate C2 is bonded to the projections T1 formed on the base semiconductor regions Bs, and a bonding surface D1 is formed therebetween. The bonding surface D1 has a loop shape in a predetermined region R1 of the base substrate B2. Thus, a space sealed in a highly vacuum condition is provided between the surface of the predetermined region R1 and the surface of the cap substrate C2 by bonding the base substrate B2 and the cap substrate C2.
Also, as the base substrate B2 and the cap substrate C2 are bonded, specific cap conductive regions Ce1, Ce2 are electrically connected to the specific base semiconductor regions Bs1, Bs2, respectively, to serve as leading conductive regions. In other words, the leading conductive regions Ce1, Ce2 are respectively connected to the movable semiconductor region Bs1 and the fixed semiconductor region Bs2, respectively.
FIG. 31 shows an example of a semiconductor device described in Publication 2. A semiconductor device 92 of FIG. 31 has a semiconductor mechanical quantity sensor element for detecting a mechanical quantity, such as acceleration and angular velocity, similar to the semiconductor device 91 of FIG. 30.
The semiconductor device 92 has a base substrate B3 provided by a SOI substrate. The SOI substrate includes a support substrate 11 made of silicon semiconductor and a poly silicon layer 12 disposed on the support substrate 11 through an oxide film 13. Sensing portions Se are formed by the poly silicon layer 12 disposed on the support substrate 11.
Similar to the semiconductor device 91 of FIG. 30, the sensing portions Se include a movable electrode and a fixed electrode. The movable electrode and the fixed electrode are provided by a beam structure, which is generally used in conventional acceleration sensors and angular velocity sensors. As the movable electrode is displaced in accordance with the applied acceleration or angular velocity, the capacitance between the movable electrode and the fixed electrode is changed. A voltage signal indicative of the change in capacitance is produced.
Further, a cap C3 is fixed to the base substrate B3 to surround the sensing portions Se. The cap C3 is bonded to the poly silicon Gayer 12 through an adhesive layer Ds made of a resin adhesive or the like. The cap C3 is provided with penetrating electrodes Ke. The cap C3 is made of silicon semiconductor in which impurities, such as phosphorous (P) and boron (B), are preferably doped so as to have electrical conductivity.
The penetrating electrodes Ke pass through the cap C3 in a direction in which a thickness of the cap C3 is measured. The penetrating electrodes Ke serve to lead electrical signals from the sensing portions Se, which are located under the cap C3, to the upper surface of the cap C3. The penetrating electrodes Ke are constituted as portions of the cap C3 having the electrical conductivity.
Further, the cap C3 is formed with grooves 15, which are referred to as air isolations, on peripheries of the penetrating electrodes Ke. The grooves 15 surround the penetrating electrodes Ke, and pass through the cap C3 in the direction in which the thickness of the cap C3 is measured.
Thus, the penetrating electrodes Ke and portions of the cap C3 on the peripheries of the penetrating electrodes Ke are insulated by means of the grooves 15. That is, the grooves 15 serve as electrically insulating portions to electrically insulate the penetrating electrodes Ke from the peripheral portions thereof in the cap C3. The penetrating electrodes Ke are in contact with the poly silicon layer 12 through connecting electrodes 51, which are made of aluminum, Al—Si or the like, to make electrical connection with the sensing portions Se.
In the semiconductor device 91 of FIG. 30, the cap substrate C2 serves as a sealing cap for protecting the mechanical quantity sensor element formed in the predetermined region R1 of the surface layer of the base substrate B2.
The cap conductive regions Ce1, Ce2 of the cap substrate C2, which are electrically connected to the base semiconductor regions Bs1, Bs2 of the base substrate B2, serve as leading conductive regions.
In such a structure, however, the insulating and separating trench 31 exist on the peripheries of the leading conductive regions Ce1, Ce2 to isolate the leading conductive regions Ce1, Ce2 from the peripheral cap conductive regions. Therefore, parasitic capacitance is produced due to the insulating and separating trench 31 being an electric substance, and is likely to affect performance of the semiconductor device 91.
In the semiconductor device 92 of FIG. 31, on the other hand, the penetrating electrodes Ke are electrically insulated from the peripheral portions in the cap C3 by the grooves 15 as the air isolations. Therefore, the electric permittivity at the grooves 15 is smaller than that at the trench 31 of the semiconductor device 91 in which the electric substance is embedded. That is, the semiconductor device 92 of FIG. 31 is less apt to generate the parasitic capacitance, as compared with the semiconductor device 91 of FIG. 30.
The semiconductor device 91 employs the cap substrate C2 made of single crystal silicon. The semiconductor device 92 employs the cap substrate C3 made of silicon semiconductor. In general, silicon is less expensive than other substrate materials, and a trench is easily formed in a silicon substrate. However, silicon has a relatively large specific resistance. Therefore, the leading conductive regions Ce1, Ce1 and the penetrating electrodes Ke are likely to increase resistance, and hence the applicable range of such semiconductor devices may be restricted.